1. Field of the Invention
This invention relates to the magnetic materials used in recording heads for disk and tape drives and more specifically to the reduction of magnetostriction in these materials.
2. Description of the Background Art
Recording heads are widely used in disk drives and tape drives for storage and retrieval of digital information. Recording heads usually have separate write and read elements. Soft magnetic material having a low coercivity and a high saturated magnetic moment is used for the poles of the write element and the shields for the read element. In a tape drive the tape is in frequent contact with the recording head. Therefore, wear resistance is an important additional consideration in a tape drive.
The shield layers and write head poles are in close proximity to the read sensor. Because of this proximity, it is important that the layers be magnetically stable. It is important for the performance of the drive that the soft magnetic material be relatively free of stress and magnetostriction because these effects can lead to magnetic instability. If the magnetic domains in the shields and poles move when subjected to extraneous fields such as fields from the write head or fields from the rotating magnetic disk (or more precisely, when the walls between different magnetic domains move, resulting in the growing or shrinking of domains), Barkhausen noise is generated and is sensed in the read element. This noise can seriously degrade the quality of the readback signal. Furthermore, when after movement the domains do not come back to their original position, the shield or pole exerts a field which is oriented differently on the sensor layer in the read element. This changes the magnetic bias on the read element leading to signal asymmetry and increased error rates. Finally, the magnetic permeability of the shields or pole layers can be reduced with this non-repeatable or hysteretic behavior of the domains and this also has a detrimental effect on the read element performance.
A common set of materials used in shields and poles are alloys of nickel and iron. For example Ni(80%)Fe(20%) has good magnetostriction but somewhat limited saturated moment (Ms≅10 kG). Increasing the Fe content increases the moment but leads to high magnetostriction. For example Ni(45%)Fe(55%) has better moment (Ms≅16 kG) but a rather high magnetostriction of about 25xc3x9710xe2x88x926. Attempts have been made in the past to laminate materials using alternate layers of materials having positive and negative magnetostriction. These films tend to have high local stress at the interfaces between layers. Another approach to develop a material with improved magnetic stability has lead to the development of alternate layers of magnetic and non-magnetic layers. The addition of a significant amount of non-magnetic material results in a significantly reduced moment for the overall laminate.
A material is needed to construct recording heads which exhibits very low magnetostriction while not sacrificing the good magnetic properties of low coercivity and high magnetic moment.
In one embodiment of the present invention a material is provided to use in forming recording heads which has reduced magnetostriction and good magnetic properties. In another embodiment of the present invention disk drives and tape drives are provided having recording heads formed from a material having reduced magnetostriction and good magnetic properties. The reduced magnetostriction in a material according to one embodiment of the present invention provides a significant improvement in the performance of the recording heads.
In a prefered embodiment the material according to the present invention is a repeating sequence of three layers. One layer is made from an alloy of NiFe. Another layer comprises FeX(N) where the (N) indicates a nitrogenated film and the additional element, X, is preferentially Ta but can be selected from a group of other elements. The third layer, disposed between the FeX(N) and NiFe layers is tantalum. The sequence of three layers is repeated to obtain the required thickness for the final material.
The material has an intrinsically smaller value of magnetostriction and the magnetostriction is usually decreased with annealing resulting in simplified processing. The material also has improved magnetic moment compared with permalloy. Other aspects and advantages of the present invention will become apparent from the following detailed description, which when taken along with the drawings, illustrate by way of invention the principles of the invention.